So called because the shape and movement of some muscles (notably biceps) were thought to resemble mice. The analogy was made in Greek, too, where mys is both "mouse" and "muscle," and its comb. form gives the medical prefix myo-. Cf. also Old Church Slavonic mysi "mouse," mysica "arm;" German Maus "mouse; muscle," Arabic 'adalah "muscle," 'adal "field mouse." In Middle English, lacerte, from the Latin word for "lizard," also was used as a word for a muscle.

Hence muscular and mousy are relatives, and a Middle English word for "muscular" was lacertous, "lizardy." Figurative sense of "force, violence, threat of violence" is 1930, American English. Muscle car "hot rod" is from 1969.

v.

1913, "to accomplish by strength," from muscle (n.). Related: Muscled; muscling. To muscle in is 1929 in underworld slang.

A tissue consisting predominantly of contractile cells and classified as skeletal, cardiac, or smooth, the last lacking transverse striations characteristic of the first two.

Any of the contractile organs of the body by which movements of the various organs and parts are effected, and whose fibers are usually attached at each extremity to a bone or other structure by a tendon.

(mŭs'əl) A body tissue composed of sheets or bundles of cells that contract to produce movement or increase tension. Muscle cells contain filaments made of the proteins actin and myosin, which lie parallel to each other. When a muscle is signaled to contract, the actin and myosin filaments slide past each other in an overlapping pattern. ◇ Skeletal muscle effects voluntary movement and is made up of bundles of elongated cells (muscle fibers), each of which contains many nuclei. ◇ Smooth muscle provides the contractile force for the internal organs and is controlled by the autonomic nervous system. Smooth muscle cells are spindle-shaped and each contains a single nucleus. ◇ Cardiac muscle makes up the muscle of the heart and consists of a meshwork of striated cells.